Laminated window panels



Dec.v 5, 1967 D. R. ORCUTT 3,356,833

LAMINATED WINDOW PANELS Original Filed Aug. D., 1963 5 Sheets-Sheet lINVENTOR.

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INVENTOR 01576' 12. O/@CUT' s/wm@ We A fram/@f5 United States Patent O3,356,833 LAMINATED WINDOW PANELS Dee R. Orcutt, Natrona Heights, Pa.,assignor to Pittsburgh Plate Glass Company, Pittsburgh, Pa., acorporation of Pennsylvania Original application Aug. 2, 1963, Ser. No.299,582.

Divided and this application Sept. 8, 1965, Ser.

3 Claims. (Cl. 219-522) This application is a division of applicationSer. No. 299,582, filed Aug. 2, 1963, now abandoned; which applicationis a continuation-in-part of application Ser. No. 275,448, filed Apr.24, 1963, now abandoned; and which latter application is acontinuation-impart of application Ser. No. 261,996, filed Mar. l, 1963,now abandoned.

This invention relates generally to improvements in the structure oflaminated Window panels comprising two 4or more sheets of rigid,transparent material alternating with plastic-interlayers that bond thesheets together and to an improved process for their fabrication.

This invention has particular relation to transparent,laminated-aircraft panels of the type that can be electrically heatedand which would normally be exposed to extremely low temperatures andpressures on at least one surface thereof during high altitude flight.

Specifically, this invention is concerned with the development ofimproved aircraft window panels and like assemblies and envisions makingcertain applications of fiberglass reinforced, thermosetting resin inthe marginal area of the panels outside their viewing area to improvetheir structure and the method for their fabrication.

In the fabrication and manufacture of laminated window panels, onematerial that is frequently used to form the rigid, transparent sheetsor plies of the laminate is glass. However, for many applications,polyester resins, acrylic resins, polycarbonate resins and Iother likematerials may be advantageously employed in forming rigid, transparentsheet material for use in the structure of laminated window panels. Forexample, a polycarbonate which has been found to be very satisfactoryfor use in laminated window panels is produced from a monomercommercially known as CR-39. The composition Of CR-39 is fully disclosedin U.S. Letters Patent 2,370,565, granted to Irving E. Muskat andFranklin Strain. Thus, for the purpose of the present invention, whenreference is hereinafter made to glass sheets or plies, used in thepanel structure, it is intended that the expression should also includerigid. transparent, resinous sheet materials.

The improvements in the panel structure contemplated by this inventionrelate to the use of a fiberglass reinforced thermosetting resintherein. Typical examples of its Vemployment are (l) as protection forelectrical terminal blocks and lead wire connections, (2) as interlayerinserts for the prevention lof delamination and/or cold chipping and forreinforcing the interlayers material, and (3) as edge frames orchanneling disposed about the periphery of the laminated aircraft panelfor edge and interlayer protection.

Generally, the laminated panels, according to the present invention,employ fiberglass reinforced thermosetting resinous material, which hasa -relatively low coefficient of thermal expansion, in the marginalportion of the assembly outside the Viewing area. The reinforcedresinous material is flexible when uncured and becomes rigid uponcuring. In fabricating such panels, the flexibility of the uncuredresinous material helps produce an intimate surface to surface contactbetween the reinforced resinous material and the other elements of thepanel when assembled for lamination. The thermosetting property of theresinous material enables it to harden while rice maintaining saidintimate surface to surface contact during the final lamination of thepanel under conditions of elevated temperature and pressure commonlydeveloped in an autoclave.

The cured, reinforced resinous material of this invention has arelatively low coefficient of thermal expansion. When finallyincorporated into the panel structure, this property of the materialprevents the development of undesirable stress concentration due toadjacent materials expanding (or contracting) at too great of adifferential rate. It has been generally found desirable for most of thedisclosed applications that the coefficient of thermal expansion of thereinforced resinous material be in a range from about 0.5 to 8.0micro-inches/inch/ F. Preferably, the coeflicient of termal expansionshould lie within a range from about 1.5 to 7.0 micro-inches/ inch/ F.Consistently good results have been obtained, however, when thecoetiicient of thermal expansion of the cured, reinforced resin-ousmaterial fell into a range from about 2.0 to 6.0 micro-inches/ inch/ F.

The proposed improvements in the panel structure have particularrelation to the problems normally encountered in electrically heatedaircraft panel designs and applications. Thus, in connection with thecontemplated uses of fiberglass reinforced thermosetting resin,consideration must be given to electrical, chemical, thermal and liquidpenetration problems as well as physical or mechanical problems inascertaining the extent of the improvements made in the panel structure.

The construction and use of electrically heated laminated panels foraircraft windows or windshields is per se well known. Generally, thepanel consists of an electrical heating circuit located between two ormore sheets of glass or other rigid, transparent plies which are` bondedtogether by a thermoplastic interlayer material, such as polyvinylbutyral, a silicone resin or interlayer material such as disclosed inapplications Ser. No. 68,942 and 68,943 of Wismer et al., filed Nov. 14,1960, for Glass- Resin Laminates. Provision is generally made formounting one or more electrical terminal Iblocks on the panel assemblyto accommodate electn'cal power connections supplying current to theheating circuit.

Specific embodiments of the above basic panel may assume various shapesand the arrangement of the panel components may vary depending uponparticular design requirements. Additional components such astemperature control sensing devices may be incorporated into the basicpanel structure.

The sheets of glass used in the panel may be of the same or differentsizes. The peripheral margins of the interlayer material m-ay be cutflush with the edges of adjacent `glass sheets and/or may extend beyondthe edges of some of the glass sheets to provide in itself a resilientmeans for supporting the laminated glass assembly. The interlayer may beprovided with inserts which have characteristics that inhibitdelamination and a phenomenon known as cold chipping. Where aninterlayer has extended portions, these portions may include interlayerinserts for reinforcement of the interl-ayer material. Electricalterminal blocks may be mounted on any desired surface of the panel whichis accessible for power lead attachment purposes when the panel has beenmounted on the aircraft body.

The present invention is directed to the solution of problems which havearisen primarily in conjunction with known aircraft designs andIapplications of electrically heated laminated glass panels, although itwill be recognized that certain embodiments described hereinbelow aresusceptible of use in laminated assemblies of rigid, transparentresinous sheet material and assemblies not prt vided with heating means.

Surface mounted terminal blocks One such problem involves the use ofsurface mounted terminal blocks requiring the extension of electricallead connections from the terminal block, across a marginal portion ofthe panel and into an interlayer for attachment with a heating -circuitand/or temperature sensing device. External lugs on the terminal blocksconnect the interior circuits of the panel to a suitable power sourcelocated elsewhere in the aircraft.

In such applications, problems have arisen in providing the requiredterminal mounting and lead wire connections by ordinary fabricationtechniques while maintaining adequate protection therefor against normalhazards incident to the specific panel design and use.

Previous attempts to provide adequate protection for surface mountedterminal blocks and lead wire connections, including provision ofinsulating sleeves about the lead wires and the application of layers ofepoxy resin bonding material, have not proved entirely satisfactory.Previous materials do not bond intimately enough to the assembly and thelead wires to furnish an effective seal against atmospheric elementssuch as water vapor, fumes from aircraft propellants, etc., and toprovide mechanical protection for the lead wires and a proper electricalinsulation to prevent their grounding.

In one aspect, this invention relates to laminated panels of the typehaving at least one terminal block mounted on an exterior surface of theassembly and lead wires extending from the terminal block yacross theexterior margin of the -assembly to an electrically conductive circuitcomprising a bus bar and a film located interiorly of the glasslaminate. It has been found necessary to extend the lead wire about theouter margin of the assembly because drilling a hole in the panel pliesand possibly other lamina of the assembly to permit a direct interiorconnecting path for the lead wire from the externally mounted terminalblock to the interior bus bar structurally weakens the panel unduly forservice in aircraft.

Briefly, this aspect of the invention is b-ased upon finding that awoven fiberglass tape or cloth impregnated with a thermosetting resincan be advantageously used in the lfabrication of the above-mentionedpanels to provide excellent electrical, mechanical yand fiuidpenetration protection and to securely bond the surface mounted terminalblock and the lead wires to the panel structure.

Interlayler inserts Another problem which has arisen with existingaircraft panel designs and applications involves delamination and whathas been commonly referred to as cold chipping. The normal constructionof aircraft windows, as pointed out above, consists of a laminate madeup of two or more plies of glass with polyvinyl butyral or likeinterlayers. The interlayers are usually relatively thick, varying from1/3 to 4A@ inch in thickness. One or more of the interlayers may extendbeyond the edges of the glass plies and may cont-ain one or morereinforcing frames or inserts of aluminum, stainless steel, or othersuitable material bonded within the interlayer, in a plane substantiallyparallel to that of the viewing surfaces of the panel, and extendinginwardly beyond the edges of the glass. The interlayer extension andreinforcing frame securely mount the panel to the aircraft body. Thereinforcing frame or insert imparts increased shear resistance to theextended portion of the interlayer in a normal installation.

The coefficient of thermal expansion of the polyvinyl butyral plastic isapproximately 6 times that of glass in the normal temperature range inwhich aircraft is used. When the laminate is exposed to extremely lowtemperatures, the difference in thermal expansion of the glass andplastic frequently causes delamination or chipping of the -glass at thebonded surfaces. Delamination occurs upon failure of the glass toplastic adhesive bond and cold chipping occurs as a result of the glassto plastic adhesive bond being stronger than the cohesive bond betweenadjacent portions of -a glass surface. Generally, cold chipping and/ordelamination originates along t-he edge of the interior surface of theglass sheets, where it is theorized that the stress concentration isgreatest. This stress concentration and consequent delamination and/ orcold chipping is even more pronounced along the edge of a larger glasssheet when the glass sheets are of unequal area. In actual aircraftapplications, this stress concentration is intensified due to thepressure differential imposed on the mounting at high altitude flying. Atemperature gradient developed by operating deicing heating circuits,located interiorly of the panel, imposes additional stress on the panel.

Previous attempts to reduce the tendency for delamination and coldchipping have been rewarded with only a moderate degree of success. Onemethod previously employed linvolves -the addition of an adhesive havinglow temperature elasticity tothe interior marginal surface areas of theglass plies adjacent to the interlayer. This layer of elastic bondingmaterial extends inwardly from the edges of the glass plies andpreferably also extends downwardly over at least a portion of the edgesof the glass plies, a distance sufficient to avoid the possibility ofgetting plastic interlayer material on the glass edge during thelaminating process. Such an arrangement and examples of elastic bondingmaterials that may be employed are fully disclosed in U.S. LettersPatent 2,697,675, granted to R. A. Gaiser.

Another method previously employed to reduce the tendency fordelamination and cold chipping is to insert a complete parting materialin the interlayer at varying depths from the inboard surfaces of theglass plies. This method and examples of complete parting materials thatmay be used are disclosed in U.S. Letters Patent 2,650,890, to W. K.Bledsoe and 2,991,207, to P. A. Miller. Cornplete parting materialsother than cellophane or pressure sensitive cellophane tape which havebeen successfully used include pressure sensitive Mylar and Teflontapes.

Both of the above two methods are based on the theory of relieveing thestress concentration before delamination and/or cold chipping occurs.

A third method involves the use of balancing inserts bonded to theinterlayer outside the margin of the smaller glass sheet to oppose themargin of the larger glass sheet that extends beyond the periphery ofthe smaller glass sheet. This solution is fully disclosed in U.S.Letters Patent 2,758,042 to R. F. Raymond et al. In this third method,the theory is to statically counterbalance the stress concentrationbefore delamination and/or cold chipping occurs.

The major deficiency of the previously used methods of reducing thetendency for delamination and cold chipping is that they cease tofunction well at extremely low temperatures, i.e., temperatures below 50F. and as low as F. Thus, a second aspect of this invention relates toimproving the resistance of heated laminated glass panels todelamination and cold chipping at extremely low temperatures.

This aspect of the invention is based on the finding that a wovenfiberglass tape impregnated with a thermosetting. resin and having athermal coefficient of expansion approximating that of glass can beadvantageously employed to form interlayer inserts in laminated aircraftpanels to impart an improved resistance to delamination and coldchipping, even at temperatures as low as 80 F.

Edge frames Aithird problem which has arisen in connection with aircraftpanel designs and applications involves providing adequate mechanicalprotection for the edges of the panel plies and also to provide adequateprotection against fluid penetration by jet fuels, ethylene glycol,moisture, etc., into the interlayer. Mechanical protection is desirableto avoid chipping or breaking the edges of the panel during normalhandling and/or installation. Protection against uid penetration intothe interlayer may involve mechanical as well as chemical considerationsand becomes necessary where fluids which would adversely affect thepanel structure may normally come in contact therewith. Freezingmoisture or fluids which would chemically react to weaken the interlayermaterial or its bond to the other structural elements of the panelassembly could obviously render the panel unacceptable for normal use.

In order to achieve desired mechanical protection and to provide amechanical and/ or chemical seal along the edges of the panel, it isnecessary to use edge frame material which is essentially chemicallyinert to normally encountered liuids, conforms well to the contour ofvarious panel designs and is mechanically strong.

Previously used edge frames are not found to be entirely satisfactoryeither because of their inherent bulk or because they were inherentlyweak in one or more of the physical or chemical properties enumeratedabove. Thus, another aspect of 4this invention has relation to providingan improved edge frame for laminated aircraft panels.

This aspect of the invention is based on the discovery that a fiberglassreinforced tape impregnated with a thermosetting resin can be conformedreadily to the contour of various panel designs with a minimum of bulkand exhibits the superior mechanical and chemical properties requiredfor aircraft panel installations.

Method Of particular importance is the discovery of an improved methodof fabrication whereby uncured resinous fiberglass tape for interlayerinserts is interleaved with the interlayer material during assemblyand/or is bent to fit the curves and angles encountered in surfacemounted terminal block and lead wire installations and/or edge frameconstruction and thereafter the resinous fiberglass tape is cured to thefinal or C stage during the step of laminating the panel sheets or pliesto produce a finished, completely assembled panel. The term uncured, asused herein, denotes the absence of the final or C stage of curing(solvent-insoluble stage) during which the resinous material exhibitslittle or no plastic flow upon heating. This term does include lesserstages of curing, e.g., A and B stage partial cures.

Therefore, an object of this invention is to provide improvedelectrically heated laminated panels having exterior lead wiresconnecting an interior electrical circuit with an exteriorly mountedterminal block.

Another object of this invention is to provide improved laminatedpanels, of the type that are normally electrically heated, which containinterlayer inserts for reinforcing the interlayer and/ or for impartingan improved resistance to delamination and cold chipping at extremelylowtemperatures. Y

Still another object of this invention is to provide improved laminatedpanels, for aircraft and like installations, having edge frames whichare highly resistant to fluid penetration, which provide mechanicalprotection for the edges during normal handling and/ or installation,and which conform very closely to the configuration of the peripheraledge of the panel.

A further obje-ct of this invention is to provide improved electricallyheated laminated panels for aircraft which will successfully withstandexposure to fluid penetration, high and low temperatures, and mechanicalhazards, encountered under normal operating conditions.

Another object of this invention is to -provide a method of fabricationwhereby surface mounted terminal connections, interlayer inserts andedge framing may be finally integrated into the panel structure duringthe laminating step in the process of the panel fabrication withoutperforming any auxiliary steps other than a conventional initialassembly with the other panel components.

These and other objects of the invention will become more apparentduring the course of the following description when taken in connectionwith the accompanying drawings.

In the drawings, wherein like numerals are employed to designate likeparts throughout the same,

FIG. l is a schematic representation in plan of a typical panel assemblyin the fabrication of which the method of the present invention can bepracticed.

FIGS. 2-4 are typical sections along a line such as II-II of FIG. lillustrating the details of various embodiments of surface mountedterminal blocks and comprises one aspect of the present invention. n

FIGS. 5-10 are typical sections along a line such as II-II of FIG. lillustrating the details of various embodiments of interlayer insertsand comprises another aspect of the present invention. In addition,FIGS. 9 and 10 illustrate various forms of combining interlayer insertswith edge framing.

FIGS. 11-13 are typical sections along a line such as II-II of FIG. 1illustrating the details of various embodiments of edge frames andcomprises still another aspect of the present invention.

In FIG. l there is shown a typical article produced in accordance withthis inventionin which a terminal block 1 is mounted on the inboardsurface of the laminated glass panel 3 which is constmcted to beelectrically heated.

The construction of electrically heated panels is per se well known. Asdisclosed in U.S. Letters Patent 2,614,944, granted to William O. Lytle,an essentially trans-parent electroconductive heating film may beprovided on a surface of one of a plurality of sheets of glass laminatedtogether by a thermoplastic interlayer. The interlayer may itself becomprised of a laminated structure of thin sheets of thermoplasticmaterial assembled together to the composite thickness required.Additionally, it is known that a heating circuit may be provided by anessentially transparent heating filament embedded within the plasticinterlayer in lieu of the electroconductive film on a glass sheetsurface, such as disclosed in U.S. Patent No.,

2,813,960 to Arthus Egle and Walther Bethge.

Bus bars extending along opposing marginal portions of one of the glasssheets are conventionally attached to the heating filament of -film fordistributing electrical power thereto. Lead wires connect the bus barsto terminal blocks located on the exterior of the panel. Electriccurrent is supplied by means of external connections from the terminalblocks to a power source (not shown).

FIG. 2 shows a typical cross-section through a portion of a panelfabricated in accordance with the practice of the present inventionshowing a surface mounted terminal block and lead wire connections andconstitutes one aspect of this invention. The sheet of glass `5constitutes the outboard glass ply of the panel 3 in its installedposition. Tlrfe sheet of glass 7, on the other hand, is the inboardglass ply of the panel 3. Interposed between the two sheets of glass isa thermoplastic interlayer 9 which bonds the glass plies together.

The interlayer 9 may be comprised of a series of thin sheets of asuitable thermoplastic material, such as polyvinyl butyral, whichultimately fuse together into a unitary body during the process oflaminating under heat and pressure. The interlayer 9 may also contain areinforcing frame or insert 11 to impart shear resistance to theextended portion of the interlayer 9 which supports the panel assembly 3in its installed position.

A heating circuit is also located on the interior surface of glass sheet5 and comprises an essentially transparent electroconductive film 10 andbus bars 12 on the glass surface facing the interlayer 9. Alternately,an essentially transparent filamentary circuit (not shown) or othersuitable heating means embedded within the interlayer may be employed.Temperature sensing devices may also be included within the panel. Thebus 'bars are connected to the heating circuit to facilitate lead wireattachments.

Lead wires 13, of which one is shown, extend from the bus bar 12 alongor through the interlayer and around the inner glass ply 7 to asurface-mounted terminal block 1. Where necessary, the interlayer issplit during the process of fabrication to permit passing lead wirestherethrough.

In one specific embodiment of this invention, as shown in FIG. 2, thelead wire 13 is covered by tWo strips of a woven fiberglass tape 15impregnated with a thermosetting resin. As will be seen by reference toFIG. 2, the tape 15 extends for some distance into the interlayer, isthen intimately conformed to the edge of the glass sheet about which thelead wire 13 traverses and finally extends along the exposed surface ofthe inner glass ply 7 to the surface-mounted terminal block 1.

One of the tapes extends a short distance beneath the terminal blockanda portion 16 is suitably undercut to provide space in the terminalblock therefor. The other tape extends completely acrossthe terminalblock and elastic bonding material 17 such as disclosed in U.S. LettersPatent 2,697,675, supra, is applied between the tape and areas of theglass along which the tape extends.

The woven fiberglass tape can be impregnated with any suitable A(Water-solubleor dispersible) or B (solventsoluble) stage thermosettingcondensate. Such condensates can be uncured (A stage) or parti-allycured (B stage), yet are always capable of further curing to the C(solvent-insoluble) stage using heat alone or a combination of heat anda curing catalyst or catalysts with or without superatmosphericpressures. The curing temperatures can range from about 100 to 400 F.with or Without catalysts to effect curing in a reasonably rapid periodof time, viz., about to about 120 minutes, using pressures up to about500 pounds per square inch, e.g., from about to about 500 pounds persquare inch, with the higher pressures being used to aid in simultaneouscuring and laminating of a thermosettable condensate which has lbeenprecured (partially cured) to a B stage prior to autoclaving (the finalstage of laminating).

Usually, however, an A stage to early B or medium B stage thermosettingcondensate is employed. Such condensates can be cured readily attemperatures of from about 200 to 360 F. and pressures ranging from 30to about 300 pounds per square inch for a 15 to 90 minute curing cycle.Preferably, the curing is conducted at temperatures of 275 to 300 F.using pressures of 150 to 250 pounds per square inch over a 30 to 40minute cure cycle to attain the final or C stage of curing.

Suitable exemplary A (essentially uncured) to B stage (partially cured)thermosetting condensates which can be employed in the practice of thisinvention include: phenol-formaldehyde condensates;resorcinol-formaldehyde condensates; melamine-formaldehyde condensates;urea-formaldehyde condensates; condensate polyblends (intimatemechanical mixtures) of phenol-formaldehyde and (l)melamine-formaldehyde, (2) urea-formaldehyde; (3)dicyandiamide-formaldehyde; interpoly-rner c0- condensates of phenol,melamine and formaldehyde, or phenol, urea and formaldehyde; etc. Alsouncured or partially cured polyester condensates can be used.

Phenolic condensates, especially A or B stage phenolformaldehydecondensates, are particularly well-suited for use in accordance withthis invention. Typically, these phenol-formaldehyde condensates in theA stage have a viscosity at C. of from 80 to 160 centipoises per second,and are readily soluble in acetone, ketones and most common organicsolvents. Suitable A or B stage phenol-formaldehyde condensates can beproduced according to conventional condensation procedures with orWithout condensation catalysts. When catalysts are used to aid andaccelerate condensation, it is customary to employ either a one-stagecondensation using a basic catalyst or a two-stage condensation usingacid catalyst. The mol ratio of formaldehyde to phenol can varyconsiderably, e.g., from 0.5 to 4.0:1. Usually, however, the mol ratioof formaldehyde to phenol ranges from about 0.7 Vto '3.021, and eitherphenol or formaldehyde can predominate on a mol basis to effectcondensation. Gener- -ally, there is some excess phenol present when thephenol- `formaldehyde condensate is in the uncured state.

Suitable condensation and/or curing catalysts which can be used to aidin advancing the phenolic condensate or condensate mixture to the final(C stage) include,

'among others, ammonium chloride, ammonium sulfate, ammonium nitrate,ammonium bromide, hexamethylene Costa Mesa, Calif. Conolon 506 phenoliccondensate preimpregnated glass fiber tape contains approximately 34percent phenol-formaldehyde condensate (6 percent volatile content) withthe remainder being glass fibers. The phenol-'formaldehyde condensatetherein in the A 'stage has a viscosity of Y80 to 160 centipoises persecond vat 25 C.

Following is a list of pertinent properties of Conolon 506 withrepresentative values assigned to each property. These values were takenfrom the results of actual tests performed on cured specimens o-fConolon 506 and published by its manufacture in bulletin LDSZABM-HR-7/60 and a technical bulletin .entitled Conolon-506.

Physical Properties: flexural strength, about 62,000

`p.s.i.; flexural modulus, about 3 106 p,s.i.

`Chemical Properties: After 30 days `water immersion: :liexuralstrength, 60,500 psi.; tensile strength, 48,400 p.s.i.; compressionstrength, 32,160 p.s.i. After 24 hours exposure in MIL-'M-3136hydrocarbon fluid standard test (Type III): flexural strength, 64,000p.s.i.; change in weight, +0.41 percent. After 24 hours exposure in MIL-E-5559 ethylene glycol: flexural strength, 65,000 psi.; change inweight, +1.02 percent.

Thermal Properties: Coefficient of thermal expansion inmicro-inches/inch/ F. between 100 F. and 300 F.: longitudinal, from4.5-5.0; diagonal (45), from 2.5- 5.0; transverse, from 4.6-5.0.

Electrical Properties: dielectric constant, (at one megacycle, dry),3.41; dielectric constant (at one megacycle, wet), 4.12.

FIGS. 3 and 4 show other embodiments of the present invention. Theessential difference between FIGS. 3 and 4 and FIG. 2 is in thearrangement of the component structures of the panel for different typesof panel mounting and/ or the number of inner and outer plies of glassused.-

In the fabrication of the panel, the various panel members are assembledto conform to the particular panel design and may, for example, displaythe relationships shown in FIGS. 2 to 4. Generally, the structure isbuilt up layer by layer beginning with vthe outer glass ply. During theintermediate steps of fabrication, the lead wire 13 is placed betweenpieces of uncured fiberglass tape which have been impregnated with athermosetting resin. An elastic bonding material 17, such as a rubberbase adhesive disclosed in the aforesaid Gaiser patent, is applied to.the areas of the glass with which the tape would normally come intocontact. Alternately, a thin vfilm of polyvinyl butyral, about .015 inchthick, may be used as the bonding material without adversely affectingthe resistance of the panel to delamination and cold chipping, to bediscussed more fully hereinafter. It has been found that a thinpolyvinyl butyral bonding film, having relatively low mass, fails todevelop a sufficient stress concentration at low tempera-tures, due tothe differential contraction of the polyvinyl butyral and the glass, tocause delamination and/ or cold chipping when the film is sandwichedbetween the glass edge and a material having a comparable coefiicient ofthermal expansion. The tape, lead wires and connected terminal block arethen placed on the elasti-c bonding material or the polyvinyl butyralfilm. In some cases, it has also been found desirable to place anelastic bonding material or polyvinyl butyral film layer between thefiberglass tape and the terminal bl-ock.

The assembled panel is then subjected to heat (about 275 to 300 F.) andpressure (about 200l pounds per square inch) for a sufficient time(about 35 minutes) to effect the lamination -of the glass plies and thesimultaneous curing of the impregnated tape.

Curing the material known as Conolon 506 produces a hard, smoothlysurfaced material having a low coefficient of expansion, good electricalinsulating properties, high mechanical strength, and excellentresistance to moisture and fluid penetration.

The uncured Conolon 506 is very flexible and capable of conforming veryintimately with the shape of the terminal block and lead wire.Therefore, this material is susceptible of initimate assembly before thepanel is laminated.

'Samples produced in accordance with the above process employing thetype mounting, insulation material and construction sho-wn in FIGS. 2 to4 have successfully withstood standard electrical insulation tests,torque tests, humidity and moisture tests, and temperature cycling testssimulating conditions encountered in normal field service f electricallyheated panels.

FIGS. -10 show typical cross-sections through a portion of a panelfabricated in accordance with the practice of the present inventionillustrating various embodiments of interlayer inserts and comprisesanother aspect of this invention. The basic panel arrangement of glassplies 5, 7 bonded together by interlayer material 9 is substantially thesame as that set forth above with reference to FIGS. 2-4. Interlayerinserts 18 are provided to resist delamination and c-old chipping. Thepanel 3 may also include a reinforcing frame or insert 11 disposedwithin the interlayer 9 to lprovide shear resistance to the extendedportion thereof after installation.

The heating circuit, terminal blocks, etc., have been omitted in FIGS.5-13 for clarity of illustration, although the invention contemplatesthat the panel may be heated.

In the embodiment of FIG. 5, interlayer inserts 18, composed of wovenfiberglass cloth or tape impregnated with a modified phenolic resin, arelaminated into the polyvinyl butyral interlayer 9 adjacent the inner andouter yglass plies. The thickness of the inserts 18 can be .010 inch orgreater. They extend from the edges or from slightly outwardly of theedges of the glass plies inwardly a distance of 1A to 3/8 inch lbeyondthe edge of the smaller ply. The inserts have their inner ends roundedwith a 1 inch radius at the corners. In the preferred arrangement,inserts 18 extend about inch inwardly from the edge of the smaller ply.The insert 18 may be cut in one piece from a sufficiently large piece ofimpregnated fiberglass cloth or may be composed of a plurali-ty ofseparate strips of impregnated fiberglass tape in overlapping orabutting relation. One impregnated fiberglass material which has beenused successfully as an insert is Conolon 506.

The phenolic fiberglass inserts 18 are located in the interlayer andspaced :015 to .025 inch from the glass surfaces. It is desirable tomaintain the thickness of the interlayer material between the glasssurface and the insert 18 as thin as is practical. This thickness islimited to .015 inch at the present time, since this is the thinnestpolyvinyl butyral interlayer sheet commercially available. The inserts18 are lassembled in the uncured state in which they are susceptible ofvery intimate surface to surface contact with the adjacent plies of theinterlayer. During autoclave pressing, the resin maintains its intimatesurface to surface contact while it is cured and forms a rigid materialhaving a thermal coefficient of expansion approximately 1 to 2 timesthat of glass.

Conolon 506 exhibits a superior bond t-o itself as well as to polyvinylbutyral and other materials when autoclave pressed.

The insert material can also be cured to the C stage before assemblyinto the laminate. In this case it is necessary to sand blast thesurface of the insert to obtain a good .bond to the interlayer material.

It is desirable to place a layer of elastic bonding material 17 on theseamed edges and which extends approximately 1/16 inch into thelaminate. This helps prevent delamination and/or the formation of chipson the relatively weaker edges of the glass. A reinforcing frame orinsert 11 may be provided at the center of the interlayer 9.

In the embodiment of FIG. 6, the panel is assembled. in the same manneras discussed with reference to FIG. 5, with the exception that thesurfaces of the fiberglass resin inserts 18 are treated on the sidefacing the center of the interlayer with a complete parting agent 19,such as a pressure sensitive cellophane, Mylar or Tefion tape, to weakenthe bond between the plastic interlayer and the inward facing surface ofthe insert. This surface treated with the complete parting agent 19extends from the outer edge of the insert to a point approximately 2/3of the total insert width. The weakened bond :in this section can beaccomplished by the addition of the pressure sensitive tape or othertypes of complete parting medium to the surfaces of the inserts when theassemblies are made with uncured resin.

When precured inserts are used, the weakened bond can be accomplished byavoiding sand blasting this particular area of the insert. An elasticparting medium 17 is also applied to the edges of the glass plate andthe panel may include a reinforcing frame or insert 11 at the center ofthe interlayer 9.

In the embodiment shown in FIG. 7, the resin fiberglass insert is usedonly in the area near the outboard glass ply 5. Part of the inboardsurface of the insert 18 is treated to weaken the bond between thepolyvinyl butyral plastic and the insert as was explained with referenceto FIG. 6. In addition, a complete parting agent 19 was incorporated inthe vinyl interlayer at a distance of .020 inch inboard from the insertand coextensive therewith. The inboard .ply of glass 7 is protected fromdelamination and chipping by the application of an elastic bondingmaterial 17 on the glass surface and extending inwardly to the samedepth as the fiberglass insert and a layer of complete parting material19 extending inwardly to the edge of the outboard ply.

The embodiment of FIG. 8 shows an assembly in which the resin fiberglassinserts 18 have been incorporated and, in addition, the reinforcingyframe or insert normally found in aircraft Windows is herein comprisedof a series of reinforcing inserts 11 of resin fiberglass materialinstead of the usual single metallic frame. The reinforcing inserts 11can be of a thickness of .01() inch or greater. The reinforcing inserts11 are interleaved with sheets of polyvinyl butyral of approximately thesame thickness as that of the inserts. The reinforcing inserts 11 bondfirmly to the vinyl interlayer 9 during autoclave pressing. An elasticbond-ing material 17 is applied to the edges of the glass plies toinhibit delamination and protect the relatively weaker edges againstcold chipping. In this embodiment, there is also shown a completeparting material 19 adjacent the edges of the .inboard ply whichseparates the elastic parting material 17 from a plastic bumper 21 of amaterial such as polyvinyl butyral and a filler block 23. The fillerblock 23 can be of pre-cured phenolic or can be made up of the resinfiberglass material.

In the embodiment of FIG. 9, the resin fiberglass inserts 18 have beenextended around `the edges of the glass plies. As in previouslydescribed embodiments, the insertsare spaced approximately .015 inchfrom the surfacesoftheglass. The thin, intermediate .015 inch polyvinylbutyrallayer may be extended over the glass edges to bond the extendedportion of the inserts to the edges of the glass plies. As pointed outabove, it has been found that athin polyvinylfbutyral bonding film,applied to the edges of the glass plies and having a relatively lowmass, has no adverseeffect on the resistance of the panel todelamination and cold chipping when the thin film is sandwiched betweenthe glass edgeand a material having a comparable coecient of thermalexpansion. Alternately, the .015 inch polyvinyl butyral layers betweenthe inserts and the glass plies can becut off at the edges of the glassandthe fiberglass resin insert 18 bonded to the edges with an elasticbonding material 17, such as employed in the Gaiser Patent 2,697,675.

T he inserts 18 may extend across a portion only of the edges, mayextend completely across the edges or their extendedportionmay'terminate along the exposed marginal surface areas of .theglass plies. Also, the bonding materialfor. the extended portion of theinserts may stop shortof the'terminal end of said extended portion. The.T hiokols, Silastics o-r like sealing materials may be used to'fill theopeningformed thereby to provide a weatherproof seal against fluidpenetration between the edges ofthe glass plies andthe extended portionof the inserts. In addition to providing protection against delaminationand cold chipping, some protection is also offered to the glass intheprevention of edge chipping during handling and installation.

. The embodiment of FIG. 10 is similar to that of FIG. 9 with theexception that the fiberglass resin insert near the outboard ply hasbeen extended beyond the edge of the glass and bent outwardly to form anopening. This opening isfilled, after lamination, withThiokol orSilastic .sealing materialsZS toform aweatherproof bumper strip aroundthe outboard `ply of glass.

Electrically heated, laminated glass panels produced in accordance withthe above process and employing the typeinterlayer inserts andconstruction shown in FIGS. 5 to l0 showed no evidence of deteriorationafter a series of exposures to temperatures of -85 F. and +225 F. Theabove panels were also subjected to the standard cold cycling'test,given to other production designs not having the resinous fiberglassinserts, and showed an improved resistance to delamination and/or coldchipping of about S400 percent. A standard cycle for a cold cycling testinvolves soaking the panel in a cold chamber maintained at 65 F. for aminimum of 2 hours and then impressing 50 percent over the rated poweron the deicing circuit until the temperature reading of a thermocoupleattached to the panel reaches about 120 F. This cycle was repeated witheach cycle immediately following'the previous cycle untilfailureoccurred. Compared to production designs, the panels of the presentinvention successfully withstood about 4 times as many of the abovecycles before delamination and/or chipping occurred. This proved thatVthe panels having Conolon 506 inserts were vastly superior to productionpanels not containing Conolon 506. inserts with respect to their abilityto withstanddelamination and cold chipping.

FIGS. 11 to 13 show typical cross-sections through a portion of a panelfabricated in accordance with the practice of the .present inventionillustrating vario-us embodiments of edge frame construction andconstitutes another aspect of this invention. The basic panelarrangement of glass plies 5, 7 bonded together by interlayer material 9is substantially the same as 'set forth above, except that there is nolinterlayer extension and the edge `frame 27 is sufficiently wide tocover all interfaces of the panel and completely encloses the marginaledge of the-panel. In FIG. 13, glass core plies-6 are used between theouter `glass ply 5 and the inner glass ply 7 and are separated byinterlayer material 9. One material which has been used -veryefectivelyfor edge framing vis Conolon 506.

Laminated glass units with edge kframes can be produced by assemblingthe glass and interlayer components in the normal manner, applying athin film of elastic bonding material 17 to the edges, then-addingmultiples of thin layers ofthe uncured resin impregnated fiberglassmaterial, evacuating the complete assembly in a-bag and then subjectingthe bagged unit-to elevated temperatures and pressure in an autoclave toreffect the lamination and cure the fiberglass resin material. In somecases it may be desirable to maintain a vacuum on the unit duringautoclave pressing-to remove gases formed when the resin is curing.

According to this aspect of the present invention, the fiberglassreinforced resinous -tape is applied about the margin of the assemblywhile uncured to -make intimate surface to surface contact-with the edgesurface of the assembly. The width of the tape is at least greater thanthe separation betweenthe extreme interfaces of the assembly so thatxthetape bridges the interfaces between the plies of the assembly as well ascovering the marginal edge surface thereof. If desired, the tape may beof sufiicient width to overlap the marginal portions of the outer majorsurfacesof the assembly. When cured, the intimate Vsurface to surfacecontact is maintained and the interfaces and interlayer material areprotected in the manner described generally above.

The resin fiberglass material is available in sheets approximately .010inch thick and in the uncuredfstate is pliable and will readily conformto irregular shaped edges and to edges where the various plies of theassemblydo not match evenly. Pressing frames may be used to contain thematerial and press to desired finished dimensions. The curedmaterialmayalsobemachined orground to finished shapes having controlleddimensional tolerances. In cured form the resin-impregnated fiberglassmaterial or the fiberglass reinforcedresinous materialhas a goodresistance to mechanical and chemical damageand a coefiicient of thermalexpansion varyingfrom 1 to 2 times that of glass.

The bonding film adhering the edge frame material ,to the glass maybeeither a thin film of polyvinyl butyral plastic,.or an elastic bondingmaterial 17 such as used inthe-previous embodiments, or a combination ofboth.

This edge frame construction appears to be most useful in laminatedglass units where protection of the plastic interlayer as well as theyglass edges (as inthe embodimentsof FIGS. 9 to 10) is desirable. It can,however, be applied to monolithic glass if required.

FIGS. 11 to 13 show typical glass constructions. Other combinationsrofglass and interlayer material with other edge configurations may be.used and will become obvious in the light ofthe variousembodimentsdescribed above.

Laminated Vglass panelsproduced in accordance with the above processand-employing the type material and construction Vshown in FIGS. 1,1 to13 were tested byzexposing them to temperatures of ,-65 F., +300 F. andto percentrelative humidityat 125 F. for as long as 3 weeks. The resultsof all tests were satisfactory and showed no visible fluid penetrationordeterioration of the panel. In contrast, the usual testfor commercialproduction` requires a maximum durationy of one week of exposure of thistype. These testsindicate that thesepanels tested meetpconditions farmore severe than those required for present commercialproducts of thistype.

Although the present invention has been described with reference tospecific details of certain embodiments thereof,` it is not intendedthat `such details shall be regarded as limitations upon the scope ofthe invention except insofar as included in the accompanying claims.

I claim:

`1. In an electrically heated, laminatedV window. panel comprising anVassembly of rigid, transparent sheets bonded together by a transparentlplastic interlayer material, the transparent sheets and interlayermaterial comprising electrically non-conductive materials, anessentiallytransparent electroconductive circuit within said assembly, bus barselectrically connected to said electroconductive circuit and lead wireextending along a margin of said assembly and electrically connectingsaid bus bars to at least one terminal block mounted on an exteriorsurface of said assembly, the lead wire, bus bars, and electroconductivecircuit being electrically connected to provide a potential dilerenceacross the electroconductive circuit when an external source ofelectrical energy is applied at the terminal block thereby causing theelectroconductive circuit to perform as an electrical heater for thewindow panel, the improvement comprising a thermosetting resinimpregnated fiberglass tape having a coeicient of thermal expansion offrom 0.5 to 8.0 microinch/inch/ F., between 100 F. and 300 F. disposedabout and enclosing said lead wire and disposed along the mountingsurface of said terminal block and cured in intimate surface-to-surface-contact with said lead wire and said mounting surface to provide goodelectrical, mechanical, and iluid penetration protection and to securelybond the surface mounted terminal block and lead wire to the panelstructure.

2. In a laminated window panel comprising a plurality of rigid,transparent sheets separated from one another by transparent plasticinterlayer material, the transparent sheets and interlayer materialcomprising electrically nonconductive materials and the rigid,transparent sheets including an inboard ply and an outboard ply, anessentially transparent electroconductive circuit within said panel, atleast one terminal block mounted on an exterior surface of said paneland lead wire electrically connecting said circuit to said terminalblock and extending at least partially along an exterior surface of saidpanel, the lead Wire and electroconductive circuit being electricallyconnected to provide a potential difference across the electroconductivecircuit when an external source of electrical energy is applied at theterminal block thereby causing the electroconductive circuit to performas an electrical heater for the window panel, the improvement comprisinga thermosetting resin impregnated berglass member having a coefficientof thermal expansion of from 0.5 to 8.0 microinch/inch/ F., between 100F. and 300 F. disposed about and enclosing said exposed portions of thelead wire and disposed along the mounting surface of said terminal blockand cured in intimate surfaceto-surface contact with said lead wire andsaid mounting surface to provide good electrical, mechanical, and fluidpenetration protection and to securely bond the surface mounted terminalblock and lead wire to the panel structure.

3. The panel of claim 2 further including a bonding material betweensaid member and portions of the panel with which said member is broughtinto contact.

References Cited UNITED STATES PATENTS 2,650,976 9/1953 Gaiser et al.219-543 2,915,490 12/1959 Hopper 161-167 2,938,103 5/1960 Crump 219-545X 3,081,205 3/1963 Shorr 161-44 2,552,955 5/1951 Gaiser et al. 219-541 X2,710,909 6/1955 Logan et al 338-212 2,884,509 4/1959 Heath 338-2082,954,454 9/1960 Gaiser 219--203 2,991,207 7/1961 Miller 219-2033,041,436 6/1962 Brady 219-203 FOREIGN PATENTS 708,242 5/ 1954 GreatBritain.

RICHARD M. WOOD, Primary Examiner.

V. Y. MAYEWSKY, Assistant Examiner.

1. IN AN ELECTRICALLY HEATED, LAMINATED WINDOW PANEL COMPRISING ANASSEMBLY OF RIGID, TRANSPARENT SHEETS BONDED TOGETHER BY A TRANSPARENTPLASTIC INTERLAYER MATERIAL, THE TRANSPARENT SHEETS AND INTERLAYERMATERIAL COMPRISING ELECTRICALLY NON-CONDUCTIVE MATERIALS, ANESSENTIALLY TRANSPARENT ELECTROCONDUCTIVE CIRCUIT WITHIN SAID ASSEMBLY,BUS BARS ELECTRICALLY CONNECTED TO SAID ELECTROCONDUCTIVE CIRCUIT ANDLEAD WIRE EXTENDING ALONG A MARGIN OF SAID ASSEMBLY AND ELECTRICALLYCONNECTING SAID BUS BARS TO AT LEAST ONE TERMINAL BLOCK MOUNTED ON ANEXTERIOR SURFACE OF SAID ASSEMBLY, THE LEAD WIRE, BUS BARS, ANDELECTROCONDUCTIVE CIRCUIT BEING ELECTRICALLY CONNECTED TO PROVIDE APOTENTIAL DIFFERENCE ACROSS THE ELECTROCONDUCTIVE CURCUIT WHEN ANEXTERNAL SOURCE OF ELECTRICAL ENERGY IS APPLIED AT THE TERMINAL BLOCKTHEREBY CAUSING THE ELECTROCONDUCTIVE CIRCUIT TO PERFORM AS ANELECTRICAL HEATER FOR THE WINDOW PANEL, THE IMPROVEMENT COMPRISING ATHERMOSETTING RESIN IMPREGNATED FIBERGLASS TAPE HAVING A COEFFICIENT OFTHEMAL EXPANSION OF FROM 0.5 TO 8.0 MICROINCH/INCH/* F., BETWEEN -100*F. AND 300* F. DISPOSED ABOUT AND ENCLOSING SAID LEAD WIRE AND DISPOSEDALONG THE MOUNTING SURFACE OF SAID TERMINAL BLOCK AND CURED IN INTIMATESURFACE-TO-SURFACE CONTACT WITH SAID LEAD WIRE AND SAID MOUNTING SURFACETO PROVIDE GOOD ELECTRICAL, MECHANICAL, AND FLUID PENETRATION PROTECTIONAND TO SECURELY BOND THE SURFACE MOUNTED TERMINAL BLOCK AND LEAD WIRE TOTHE PANEL STRUCTURE.